Water-based bottle labeling adhesive

ABSTRACT

Water-based adhesives specifically formulated for the application of transparent plastic labels onto glass substrates. The adhesive film has a clear, transparent appearance and leaves a no-label look on the bottle to which the label has been applied.

FIELD OF THE INVENTION

[0001] The invention relates to the field of adhesives. Morespecifically the invention relates to aqueous adhesives useful inbonding labels to a substrate, in particular, transparent plastic labelsto a glass bottle.

BACKGROUND OF THE INVENTION

[0002] Both natural polymers and synthetic polymers have been used asbase polymers in bottle labeling adhesive applications. Naturalpolymer-based adhesives, such as starch- and casein-based adhesives, canbe formulated to offer such advantages as good machinability, high wetstrength, and ice water resistance. While synthetic polymer-basedadhesives provide advantages such as, for example, a fast set time,natural polymer-based adhesives are often preferred due to their safety,cost and ease of handling.

[0003] While paper labels have traditionally been used for glass bottlelabeling in the food and brewery industries, an interest exist withinthe labeling industry to move away from traditional paper labels towardplastic labels, in particular, transparent plastic labels. One appealingbenefit of using a transparent plastic label is its “no-label”appearance. Environmentally, the use of labels made of a syntheticplastic material helps to preserve natural resources by reducing theconsumption of wood.

[0004] Only solvent-based adhesives have been used for the applicationof plastic labels to glass substrates such as bottles. A water-basedadhesive capable of such use has never, heretofore, been formulated.This is due to (1) differences in surface properties of the plastic andglass substrates which makes it difficult to hold a plastic label onto aglass surface, (2) adhesive film concealed between the plastic label andglass substrate requires an extremely long time to set the label, (3)there is no where for the aqueous phase of the adhesive to go, and (4)films (either wet or dried) of many water-based adhesive are nottransparent enough when applied between a plastic label and a glasssubstrate.

[0005] A need exists in the art for a water-based adhesive which isuseful in bottle labeling applications and can advantageously be use toapply a plastic label to a glass substrate. The current inventionaddresses this need.

SUMMARY OF THE INVENTION

[0006] The invention provides a water-based adhesive specificallyformulated for the application of transparent plastic labels onto glasssubstrates. The adhesive film has a clear, transparent appearance andleaves a no-label look on the bottle to which the label has beenapplied.

[0007] One aspect of the invention is directed to a naturalpolymer-based adhesive formulation that is particularly advantageous foruse in bottle labeling applications. The adhesive of the inventioncomprises a starch component and a gelatin/animal glue component. Thestarch component may desirably comprise at least two substantiallydifferent types of starch, such as both a high amylose containing starchand a starch having a high amylopectin content. Adhesives of theinvention also, preferably, will contain a liquifier, a curing agentand/or a humectant or plasticizer, and may further, if desired, containa blowing agent, a viscosity modifier, an anti-foamer and/or apreservative. Water is used as the adhesive carrier. One preferredadhesive comprises a modified waxy starch, a hydrolyzed potato starch,gelatin, zinc carbonate, urea, and dicyandiamide.

[0008] Another aspect of the invention is directed a method for bondinga first substrate to a second substrate comprising applying to a surfaceof at least one of said first and/or second substrate the adhesivecomposition of the invention. Preferably, the first substrate is a labeland said second substrate is a container. Particularly preferred for usein the method of the invention are plastic labels and glass containers,such as jars, bottles and the like.

[0009] Still another aspect of the invention is directed to an articlecomprising a label, wherein the label is attached to the article by theadhesive described herein. A preferred embodiment of the article of theinvention is a glass article comprising a plastic label, in particular,a transparent plastic label.

DETAILED DESCRIPTION OF THE INVENTION

[0010] Various performance properties are required of an adhesive usedin a high-speed labeler. Two are of particular importance, (1) adhesivestrength and (2) a mechanical compatibility of the adhesive to anactually employed high-speed labeler. In applying paper labels tocontainers, high-speed machines (labelers) are used which transferadhesive films, while wet, to pallets which then pick labels from labelstacks and transfer the adhesive to the label. Once coated with adhesivethe label is contacted with the container for permanent adhesion.

[0011] The invention provides an adhesive, a method for bonding a firstsubstrate to a second substrate, and articles manufactured using theadhesive of the invention. A preferred method of the invention is amethod for bonding a label to a container at high line speeds.

[0012] The invention provides the labeling industry with new kinds ofwater-based adhesives that are particularly useful for applying plasticlabels onto glass containers. The adhesive has strong tack to hold theplastic label on the glass substrate and satisfactorily secures theplastic label to the glass within a reasonable time, and provides a“no-label” look due to its clarity. Moreover, the water-based adhesiveof the invention may be applied using conventional high-speed labelers,in particular pallet transfer rotary labelers of the type manufacturedby Krones, Ltd. This makes it possible for customers to move fromtraditional paper labels to plastic labels without any modification onthe production line.

[0013] The adhesive of the invention comprises a starch component and agelatin component. Preferred adhesives for use in the practice of theinvention may further comprise curing agents, humectants, plasticizers,blowing agents, liquifiers, viscosity modifiers, antifoaming agents,preservatives, thickeners, salts, crosslinkers, tackifiers, filler,bleaching agents, optical brighteners, UV indicators and peptizing saltssuch as magnesium chloride and sodium nitrate, and/or resin emulsions toprovide the required tack, overall adhesion, solution viscosity,stability, and/or desired rheological characteristics.

[0014] All starches and flours (hereinafter “starch”) may be suitablefor use as the base starch. The starch material used as the startingbase material may be obtained from any source. By “base” starch is meantraw, native or natural starch, i.e., starch as it comes from the plantsource. Such base starch include natural starches as well as geneticallyaltered and hybrid starches. Included are starches derived from a plantobtained by standard breeding techniques including crossbreeding,translocation, inversion, transformation or any other method of gene orchromosome engineering to include variations thereof. In addition,starches derived from a plant grown from artificial mutations andvariations of the above generic composition which may be produced byknown standard methods of mutation breeding are also suitable for use asthe base starch herein. Typical sources for the base starches arecereals, tubers, roots, legumes and fruits. The native source can bemaize (corn), pea, potato, sweet potato, banana, barley, wheat, rice,sago, amaranth, tapioca, arrowroot, canna, sorghum, and waxy or highamylose varieties thereof. A starch known in the art as waxy maize,which is a genetic hybrid, may advantageously be used in the practice ofthe invention. As used herein, the term “waxy” is intended to include astarch or flour containing at least about 95% by weight amylopectin andthe term “high amylose” is intended to include a starch or flourcontaining at least about 40% by weight amylose.

[0015] Chemically modified starches may also be used as the base starch.Such chemical modifications are intended to include, without limitation,crosslinked starches, acetylated and organically esterified starches,hydroxyethylated and hydroxypropylated starches, phosphorylated andinorganically esterified starches, cationic, anionic, nonionic, andzwitterionic starches, and succinate and substituted succinatederivatives of starch. Procedures for modifying starches are well-knownand described, for example in Modified Starches: Properties and Uses,Ed. Wurzburg, CRC Press, Inc., Florida (1986).

[0016] Physically modified starches may also be used as the base starch,including, without limitation, thermally inhibited or pregelatinizedstarches. Procedures for preparing thermally inhibited starches aredisclosed, for example, in U.S. Pat. No. 6,221,420, and referencesdisclosed therein, the disclosure of which is incorporated by reference.Exemplary processes for preparing pregelatinized granular starches aredisclosed in U.S. Pat. No. 4,280,851, U.S. Pat. No. 4,465,702, U.S. Pat.No. 5,037,929, and U.S. Pat. No. 5,149,799, the disclosures of which areincorporated by reference.

[0017] The starch component may desirably comprise at least twosubstantially different types of starch, such as both a high amylosecontaining starch and a starch having a high amylopectin content.Commercially available high amylose starches which may be used in thepractice of the invention include hydrolyzed potato starches such asSolvicol GP45 (available from Avebe) and Collys BR (available fromRoquette). Commercially available high amylopectin containing starcheswhich may be used in the practice of the invention include modified waxystarches such as Dexylose 1231 (available from Roquette) and Purity SCSA(available from National Starch and Chemical Company). The starchcomponent preferable comprises from about 10 to about 50% by weight ofthe adhesive formulation. Preferably, the high amylopectin starchrepresents all or at least the major portion of the starch component,typically in the range of from about 15 to 35% of the adhesiveformulation.

[0018] The term gelatin is used herein to include animal glues, boneglues, hide glues and the like. Such compounds are organic colloidpolymers derived from collagen, a protein constituent of animal skins,connective tissue, and bones, principally of cattle origin. There aretwo general types of gelatin. Type A is derived from collagen withexclusive acid pretreatment. Type B is the result of alkalinepretreatment of the collagen. Both types of gelatin may be used in thepractice of the invention. The gel-strength of the gelatin used can befrom weak to high strength, but preferably medium to medium/high(typically around 200 bloom). Gelatin compounds which can be used in thepractice of the invention, such as Gelatin Technical 490C arecommercially available from Lijmfabriek Trobas. The gelatin componentpreferable comprises from about 1 to about 10% by weight of the adhesiveformulation, more preferably from about 3 to about 7%.

[0019] Examples of suitable curing agents include polybasic acids andtheir anhydrides, polymerizable unsaturated acids, and mercaptans. Othersuitable curing agents include nitrogen containing compounds andaromatic polyamines. Other useful curing agents include chloro-, bromo-,and fluoro-containing Lewis acids of aluminum, boron, antimony, andtitanium, such as aluminum trichloride, aluminum tribromide, borontrifluoride, antimony pentafluoride, titanium tetrafluoride, and thelike.

[0020] Liquifiers include, but are not limited to, dicyandiamide,calcium chloride and sodium nitrate. Dicyaniamide is commerciallyavailable from Asahi Denka Kogyo K. K. under the trade name Hardener3636AS. Amounts of from about 0.5% by weight up to about 5% are typicalfor use in the practice of the invention.

[0021] The particular salt, when used, is not critical, and can beselected from many available salts. Nonlimiting examples includemagnesium chloride, sodium chloride, sodium nitrate and ammoniumacetate. The salt is typically used in amounts up to about 3% by weight.Amounts of about 0.25% to about 1.5% are preferred.

[0022] Cross-linking agents include, but are not limited to, zinccarbonate, zinc oxide and glyoxal (Ethanedial). Up to about 3% of thecross-linking agent is generally used in the practice of the invention.

[0023] The humectant used may be any of those conventionally used informulating adhesives. Typical humectants include sugars, sorbitol,glycerin and related derivatives, urea, propylene glycol and similarrelated glycols and glycol ether. The humectants are used in theadhesive formulation at levels of about 1% to about 30% by weight, andtypically from about 3% to about 20%, more preferably from about 5% toabout 15%.

[0024] Resin emulsion may be used to provide better wet-tack. Ideally,the resin emulsion is chosen from those homopolymers or copolymers thathave been dextrin-stabilized. The amount of resin emulsion used is fromabout 0 to about 40% by weight, typically from about 5 to about 20%.Non-limiting examples include ethylene vinyl acetate and polyvinylacetate that are dextrin, surfactant or polyvinyl alcohol stabilized,and others that are compatible. It is noted that the choice of resinemulsion may effect the degree of clarity of the resulting adhesive.

[0025] Preservatives for use herein include those conventionally used inaqueous adhesives such as benzoates, amides and fluorides such as sodiumfluoride. Also included are the hydroxybenzoic acid esters such asp-hydroxybenzoic acid methyl ester or p-hydroxybenzoic butyl ester.Commercially available preservatives which may be used in the practiceof the invention include KATHON LXE sold by Rohm & Haas Compan andNipacide OBS sold by Clariant. The preservative will generally beincluded in amounts of from 0.1% to about 0.2% by weight.

[0026] Adhesives of the invention generally will comprise from about 1to about 10 parts gelatin, from about 10 to about 50 parts starch.Preferred adhesives will typically also comprise up to about 3 parts ofa crosslinker such as zinc carbonate, from about 0.05 to about 1 part ofan defoamer such as Belvaloid, from about 1 to 30 parts of a humectantsuch as urea, from about 0.5 to about 5 parts of a liquifier such asdicyandiamide, and water to make up to 100 parts. When a combination ofa high amylose starch and high amylopectin starch is used, the majorportion is preferably the high amylopectin portion of the starchcomponent.

[0027] Generally, the adhesives of the invention may be made by mixingthe components as described in further detail in the Examples. The orderof addition is not critical. Cooking temperatures will generally begreater that 70° C., typically up to about 95° C. for periods of up toabout 90 minutes or longer. The viscosity of the product is thenadjusted e.g. through addition of extra water, liquifier (e.g.dicyanoamide) and/or humectant (e.g. urea) to lower the viscosity to thepreferred range of between about 40,000 cps up to about 150,0000 cps,preferably between about 70,000 cps and 120,000 cps.

[0028] While the adhesive finds particular use as a labeling adhesive,other uses are clearly contemplated and are encompassed by theinvention. The adhesive described herein may be used to for, e.g.,laminating, in particular, where two substrates require bonding and theresultant bond should have a clear appearance.

[0029] As used herein, a “container” means a jar, bottle, can orcanister, bucket, beaker and the like. The container may be made ofglass, plastic or metal. Specific examples include, but are not limitedto soft drink bottles, beer bottles, wine bottles, salad dressingbottles, sauce jars, condiment jars, and the like. The container may bemade of any type of material including but not limited to wood, glass,metal, plastic or poly and plastic-coated glass.

[0030] As used herein and a “label” means e.g. a material having asurface to which an adhesive is applied. The label may be made of anytype of material, including but not limited to paper, plastic ormetallized paper and the like. Labels may be of any size or shape. Whilethe label may be opaque, a preferred embodiment is transparent plasticlabels.

[0031] Use of the adhesives of the invention to bond plastic labels toglass substrates is particularly advantageous. A preferred embodiment ofthe invention is the use of the adhesives of the invention to bondtransparent plastic labels to glass substrates.

[0032] By “transparent” means that at least a portion of the label issubstantially clear, i.e., the surface of the substrate to which thelabel has been applied is visible through the label and adhesive.

[0033] Plastic as used herein refers to the material used to make e.g.,food and other storage containers and/or labels include polyethylene,polypropylene, polystyrene, polycarbonate, polyvinylchloride, highdensity polyethylene (HDPE) and polyethylene terephthalate (PET).

[0034] To attach the labels to the article, the adhesive is applied tothe surface of the container or, when using a high speed labeler,directly to the label. The label and the article are then contactedunder pressure and the adhesive bond allowed to set. The amount ofpressure and the time need to set the bond will depend upon the type ofcontainer, label, and the particular adhesive formulation used.

[0035] The following examples are for purpose of illustration and notintended to limit the scope of the invention in any manner.

EXAMPLES Example 1

[0036] 52% water, 0.2% defoamer, 0.9% zinc carbonate and 12% urea weremixed (e.g. in a vessel with a rotating agitator) until homogeneous,after which 7.8% Collys Br and 23.5% Dexylose I 231 were added. Themixture was then heated to 72° C. and held at this temperature for 20mins. The mixture was then cooled to 65° C. and 0.6% ammonium acetateadded. 3% Bone glue was then added between 60 and 65° C. and the finalmixture cooled to room temperature.

Example 2

[0037] 47% water, 0.2% defoamer, 0.9% zinc carbonate and 15% urea weremixed (e.g. in a vessel with a rotating agitator) until homogeneous,after which 5% gelatine was added, followed by 7.8% Solvicol GP45 and23.5% Dexylose I 231. The mixture was then heated to 72° C. and held atthis temperature for 20 mins. The mixture was then cooled to 65° C. and0.6% ammonium acetate added, and the final mixture cooled to roomtemperature.

Example 3

[0038] 47% water, 0.2% defoamer, 0.9% zinc carbonate and 15% urea weremixed (e.g. in a vessel with a rotating agitator) until homogeneous,after which 5% gelatin was added, followed by 7.8% Solvicol GP45 and23.5% Dexylose I 231. The mixture was then heated to 80° C. and held atthis temperature for 90 mins. The mixture was then cooled to 65° C. and0.6% ammonium acetate added, and the final mixture cooled to roomtemperature.

Example 4

[0039] 53% water, 0.2% defoamer, 0.9% zinc carbonate and 7% urea weremixed (e.g. in a vessel with a rotating agitator) until homogeneous,after which 2% dicyandiamide added and the mix stirred, 5% gelatine wasthen added, followed by 7.8% Solvicol GP45 and 23.5% Dexylose I 231. Themixture was then heated to 80° C. and held at this temperature for 60mins. The mixture was then cooled to 65° C. and 0.6% ammonium acetateadded, and the final mixture cooled to room temperature.

Example 5

[0040] The viscosity of the adhesive mixtures prepared in Examples 1-4were adjusted by the addition of urea and/or water, or the like to adesired viscosity. The adhesive samples were coated onto a transparentplastic label. The label was then applied to a glass jar and allowed todry. The adhesive exhibited good wet tack. Dried adhesive wassubstantially clear, with the glass substrate visible through the driedadhesive.

[0041] Many modifications and variations of this invention can be madewithout departing from its spirit and scope, as will be apparent tothose skilled in the art. The specific embodiments described herein areoffered by way of example only, and the invention is to be limited onlyby the terms of the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. An adhesive comprising a starch component, a gelatin component andwater, said adhesive being substantially clear when dried.
 2. Theadhesive of claim 1 wherein the starch component comprises at least twosubstantially different types of starches.
 3. The adhesive of claim 2wherein the starch component comprises a high amylose starch and a highamylopectin starch.
 4. The adhesive of claim 1 further comprising acrosslinking agent, a liquifier and a humectant.
 5. The adhesive ofclaim 4 which further comprises urea, dicyandiamide and zinc carbonate.6. A method for bonding a first substrate to a second substratecomprising applying to a surface of at least one of said first and/orsecond substrate the adhesive composition of claim
 1. 7. The method ofclaim 6 wherein said first substrate is a label and said secondsubstrate is a container.
 8. The method of claim 7 wherein the adhesiveis applied to a surface of the label.
 9. The method of claim 8 whereinsaid label is made of plastic and said container is a bottle or jar. 10.The method of claim 9 wherein at least a portion of said plastic labelis transparent.
 11. The method of claim 9 wherein said bottle or jar ismade of glass.
 12. The method of claim 9 wherein the plastic is selectedfrom the group consisting of polyethylene, polypropylene, polystyrene,polycarbonate, and polyvinylchloride.
 13. An article comprising a label,wherein the label is attached to the article by the adhesive of claim 1.14. The article of claim 13 which is a container.
 15. The article ofclaim 13 wherein the container is a glass container
 16. The article ofclaim 13 wherein the label is a plastic label.
 17. The article of claim16 wherein at least a portion of said plastic label is transparent.